I suppose it's an alien concept to people who lack community, but they're vital in many neighborhoods.
...since it appears some people don't know...
There isn't one job for community organizers, but generally they're advocates and mediators for people in their neighborhoods, both acting in the interest of their neighborhood in general and helping people and families at the more individual level. They work to get both city and nonprofit attention to the needs of the neighborhood, try to provide greater voice and representation for residents, they help people link up with information and programs they need, they help people deal with day to day bullshit when they get in over their heads (things like tax help, dealing with creditors, etc...). Sometimes organizing is more explicitly oriented to a specific goal, and sometimes it's just adding a bit of glue to hold a neighborhood together. People looking out for you and your neighborhood. Your local lobbyist.